Production of aluminium metal typically involves the electrolytic reduction of alumina in cells or pots. The electrolyte is made up of molten cryolite and other additives. The electrolyte is contained in a carbon and refractory lining in a steel potshell. The electrolytic cell includes a carbon anode with the lining of carbon coated in refractory material constituting the cathode. Over time the effectiveness of the lining deteriorates and the lining of the pot is removed and then replaced with a new lining. The lining material that has been removed from the pot is referred to a spent potliner (SPL).
The nature of the aluminium reduction cell process results in the formation of various carbides and nitrides within the reduction cell contents (eg refractory lining and carbon cathode and anode).
As an example, at dull red heat and above, many metals such as calcium, aluminium and silicon readily form nitrides.e.g. 2Al+N2→Al2N2 
At elevated temperatures, such metal oxides also react with carbon to form carbides.2Al2O3+9C→Al4C3+6COCaO+3C→CaC2+CO
Under these conditions various carbon-nitrogen compounds are also produced in the forms of cyanides, both simple and complex forms.
The spent pot lining materials are also high in soda, and exhibit a pH in the vicinity of 11. This caustic soda is hygroscopic, and absorbs atmospheric water (humidity) which renders it mobile and so able to react with other components of the SPL stockpiles.
SPL is hazardous because of—                Health and environmental hazards due to the presence of cyanide formed as a result of the reaction of nitrogen from air with the carbon lining.        Reactive components that combine with water to give of ammonia, methane and hydrogen which presents a potential explosion hazard.        
Disposal of SPL has been a problem for many years. In the past it was used as landfill but is now viewed as not environmentally friendly and thus its use as landfill has been banned in many countries. Consequently there have been many proposals to treat and handle SPL. Most of these proposals create some residual waste which can be used as landfill.
This invention comes about from the appreciation that SPL is potentially valuable because of the calorific value of the carbon that it contains and the presence of minerals such as alumina, fluorides, silica and sodium that can be used in other industries.
It is these issues that have brought about the present invention.